Additional typos in ‘crosstalk_pix_map’ functions

[CesileyKing]

In MMTModules.py lines 1599-1602, 1673-1676, 1748-1751, 1824-1827, and 1900-1903, the = signs should be +=. With just the = sign, if the crosstalk happens to leak into the center pixel, this overwrites the signal at the center pixel instead of adding to the signal there.